CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable.
Not Applicable.
The invention is generally related to viscometers and more specifically to viscometers employing an inductive displacement sensor to detect the angle of displacement of a bob used to measure viscosity of a tested fluid.
Viscometers are known to use a variety of configurations to measure rheological properties of a fluid. One frequently employed configuration is a rotational Couette geometry viscometer comprised of a cylindrical bob positioned on a bob axle and a concentric sleeve exterior of the bob suspended from a viscometer housing into a container holding a sample of the fluid to be tested. As the concentric sleeve is rotated at a determined speed, a specified shear rate is exerted on the fluid near the face of the rotor and rotation of the bob is induced. A biasing spring resists rotation of the bob and axle. The resulting deflection of the bob in response to the rotation of the sleeve is an indicator of the viscosity of the fluid intermediate the bob and sleeve.
Prior art viscometers include:
U.S. Pat. No. 3,751,975 issued to Katsura on Aug. 14, 1973, discloses a pair of magnetic electrical signal generators mounted on opposite ends of the torsion area of a torsion bar. When the torsion bar is rotated with one end submerged in a sample fluid, comparison of the difference between the generated signals provides a direct relationship to the viscosity of the sample fluid.
U.S. Pat. No. 4,043,183 issued to Higgs et al. on Aug. 23, 1977, discloses a consistometer for continuously measuring the viscosity of the liquid in a stream. When a reference sensor outside the stream and a detector sensor within the stream are simultaneously spun in relationship to respective stationary sensors, comparison of the difference between the reference signal and the detected signal provides a direct relationship to the viscosity of the liquid in the stream.
U.S. Pat. No. 4,175,425 issued to Brookfield on Nov. 27, 1979, discloses a viscometer having a drive cylinder and a driven cylinder attached to a resistance unit, which is linked to a magnetic transducer readout device. The patent states that the inventive structure works with other types of readout devices.
U.S. Pat. No. 4,448,061 issued to Brookfield on May 15, 1984, and reexamined on Oct. 9, 1990 and Nov. 21, 1995, discloses a rotational viscometer, which uses a rotor-stator configuration to produce continuous out-feed of electric signals of strengths varying with the viscosity of the liquid being monitored.
U.S. Pat. No. 4,484,468 issued to Gau et al. on Nov. 27, 1984, discloses an automatic rotational viscometer comprised of a rotated or torqued sleeve. The sleeve applies rotation to a bob, monitored by an optical encoder, which measures the angular displacement of the bob from the zero azimuth position and continues to be sensed until the angle is stabilized.
It would be an improvement to the field to adapt a viscometer with a linear inductive angular displacement sensor to more precisely quantify the amount of force imparted to the bob by the fluid in relationship to the rotation of the bob axle.
Accordingly, the objects of my invention are to provide, among other things, a rotational viscometer that:
provides a high degree of accuracy over the operational range;
comprises mechanically and electrically simple configuration;
is tolerant of variations in environmental conditions; and
provides reduced friction forces to the bob and axle.
Other objects of my invention will become evident throughout the reading of this application.
My invention is a rotational viscometer, which employs an electrical field sensor to measure the induced angle of rotation of a bob by a sample substance. The viscometer includes a generally circular bob attached to a bob axle, a concentric sleeve exterior of the bob, a motor for inducing rotation in the sleeve, a biasing spring attached to the bob axle for resisting axle rotation, and a measurement system comprising an electric field transmitter, an electric field receiver and a rotor extending intermediate the transmitter and receiver. The rotor is attached to the bob axle so that rotation of the bob axle and the rotor results in a measurable deviation of the received electrical field. The processor calculates the angle of displacement of the bob and transmits readable output of a sample characteristic in accordance with determined calculations based on, among other things, the sleeve rotation velocity and the bob displacement.